Call them drones ; call them toy airplanes with digital cameras dropped into their girths .

Either way , South Korean defense officials said on Friday they were sure that they came from North Korea and that they were up to no good .

Three diminutive single-engine unmanned propeller planes that look like they could have come from a hobby shop were found on the ground in March and April in parts of the South near the border with the northern Communist regime .

Though the low-tech buzzers do n't seem to represent a major danger , they come in the shadow of North Korean missile launches and the impending countdown to the test of a nuclear device .

And they made it through South Korean air defenses .

Ministry of National Defense officials in Seoul immediately suspected that the sky-blue colored fliers belonged to Pyongyang . They formed an investigation team with the United States in mid-April to analyze the `` travel log file '' and photos taken by the drones and announced the results on Friday .

Scientists found a `` smoking gun that all three were sent from North Korea and are programmed to return to North Korea , '' South Korean defense spokesman Kim Min-soek said .

Photos the drones took along on their journey corroborate their flight path , he said .

Precarious cargo

Had the mechanical carrier pigeons made it back home , they would have delivered precarious cargo , but it would have been far from precious .

Japanese-made digital cameras , which look like they could be of the consumer variety , were inserted into the bellies of the drones and had taken aerial photos of the South from around the border region .

All three were programmed to fly over military facilities , and two of them had images of targets of military interest -- strategically important islands near the demilitarized zone , and the Blue House , residence and office of South Korea 's President Park Geun-hye .

Images from the third drone were not available to South Korean investigators . A wild ginseng digger had stumbled upon the plane and had deleted its memory card so he could use it himself , the Korea Times reported .

The planes were not capable of transmitting images back to North Korea in real time , and the photos themselves were no better than what one might see on a service akin to Google Earth , Kim said in a previous briefing .

Limited capabilities

There is little danger the drones could have made it far into South Korea .

The type of drone is not used for long-range missions , a defense analyst said . Instead they 're better suited to see what the enemy is up to on the other side of a hill or wall .

`` It has quite a small range , it does n't have very long endurance so it would only be up there for a few hours . You would use those to see what the other guys are doing in a battlefield environment , '' said James Hardy , the Asia Pacific editor of IHS Jane 's Defence Weekly magazine .

`` They 're very much closely built off a remote-controlled aircraft that you can buy in a toy store . They 're just a militarized version of that , '' Hardy said .

The Korean drones are nowhere near as sophisticated as those used by the United States in Pakistan , Yemen and Afghanistan , he said .

They would also not make much of a weapon , if someone decided to stuff explosives into them , Kim has said .

`` Even if they are to be used for future attacks , -LRB- they -RRB- can only carry 2-3 kilograms of TNT and can not cause huge damage . ''

North Korea has flaunted similar , larger UAVs at military parades in recent years , and some of them have been spiked with explosives , Hardy said .

Video footage shows North Korean exercises using them as missiles , but it 's an expensive way to build a bomb , he said . And it could only take out a single vehicle or ship .

'T is the season

Spring is traditionally a time of high tensions between Pyongyang on the one side and Seoul and Washington on the other .

Annual U.S.-South Korean joint military drills , that ended on April 7 , drew criticism from North Korea , which views the exercises as `` dress rehearsals for invasion , '' according to analyst James Person from the Woodrow Wilson Center .

In March , Pyongyang fired two mid-range ballistics missiles off its eastern coast , in an apparent response to the drills . Days later , the two sides fired hundreds of shells across the Northern Limit Line , their disputed maritime border .

The shells were shot into the sea , not at hard targets .

North Korea also warned it was preparing to test another nuclear device .

`` It 's all good stuff because it allows the North Koreans to do something provocative and slightly annoying which might embarrass South Koreans , but it 's not provocative enough to create a proper military response , '' Hardy said .

Slipping through

The drones would fit well into that category , since they slipped through South Korean air defenses .

They are made of polycarbonate , which is difficult to detect with radar , according to South Korea 's Yonhap news agency .

They fly at an average speed of about 110 km per hour -LRB- 68 mph -RRB- at an altitude of 1.3 km -LRB- .8 miles -RRB- .

They were launched in North Korea from three locations , South Korea 's defense ministry said : Near the Kaesong area , 27 kilometers southeast of Haeju and 17 kilometers from Pyonggak .

South Korea 's defense ministry called the intrusion by the drones a violation of the truce that ended the bloody conflict between North and South Korea in 1953 .

Kim said Seoul will send a warning via the United Nations to Pyongyang and tighten air defenses as a response to the drones .

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Three diminutive single-engine unmanned propeller planes were found in March and April

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They look like hobby shop model airplanes with consumer cameras shoved into them

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They do n't have strong military or spy capabilities , but they made it through air defenses

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Spring is typically a time of high provocations between North and South Korea